1. Field of the Invention
The present invention relates to a catalyst for the production of nitriles. More particularly, it relates to an improved catalyst for the production of nitriles from alkanes as starting material.
2. Discussion of Background
Nitriles such as acrylonitrile and methacrylonitrile have been industrially produced as important intermediates for the preparation of fibers, synthetic resins, synthetic rubbers and the like. The most popular method for producing such nitriles is to subject an olefin such as propylene or isobutene to a catalytic reaction with ammonia and oxygen in the presence of a catalyst in a gaseous phase at a high temperature.
On the other hand, in view of the price difference between propane and propylene or between isobutane and isobutene, an attention has been drawn to developing a method for producing acrylonitrile or methacrylonitrile by a so-called ammoxidation reaction method wherein a lower alkane such as propane or isobutane is used as starting material, and it is catalytically reacted with ammonia and oxygen in a gaseous phase in the presence of a catalyst.
For example, there have been reports on a Mo--Bi--P--O catalyst (Japanese Unexamined Patent Publication No. 16887/1973), a V--Sb--O catalyst (Japanese Unexamined Patent Publication No. 33783/1972, Japanese Examined Patent Publication No. 23016/1975 and Japanese Unexamined Patent Publication No. 268668/1989), a Sb--U--V--Ni--O catalyst (Japanese Examined Patent Publication No. 14371/1972), a Sb--Sn--O catalyst (Japanese Examined Patent Publication No. 28940/1975), a V--Sb--W--P--O catalyst (Japanese Unexamined Patent Publication No. 95439/1990), a catalyst obtained by mechanically mixing a V--Sb--W--O oxide and a Bi--Ce--Mo--W--O oxide (Japanese Unexamined Patent Publication No. 38051/1989). Further, the present inventors have reported on a Mo--V--Te--Nb--O catalyst (Japanese Unexamined Patent Publication No. 257/1990 and U.S. Pat. No. 5,049,692).
However, none of these methods is fully satisfactory in the yield of the intended nitriles. In order to improve the yield of nitriles, it has been proposed to add a small amount of an organic halide, an inorganic halide or a sulfur compound, or to add water to the reaction system. However, the former three methods have a problem of possible corrosion of the reaction apparatus, while the latter water-adding method has a problem of formation of by-products by side reactions or a problem of their treatment. Thus, each method has a practical problem for industrial application.
Further, methods using the conventional catalysts other than the Mo--V--Te--Nb--O catalyst reported by the present inventors, usually require a very high reaction temperature at a level of 500.degree. C. or higher. Therefore, such methods are disadvantageous in terms of reactor material, production cost, etc.